The process of encoding color information in the scene on a black and white film had its genesis just before the turn of the twentieth century. In 1899, R. W. Wood published the results of his experiments on the use of diffraction gratings in color image formation. Later over the decades, various efforts in articulating the single frame color encoding concept gradually faded into the backdrop with the development of the multi-layer dye film processes. Recently the consumer electronics industry has introduced new products such as, video cassettes and video discs, in the consumer market for use with the home television receivers. The marketing of economical and practical home television cameras for in-house recording and playback is now within the realm of reality. The advent of video cassettes, video discs, and home television cameras has once again evoked the interest of the consumer electronics industry in the single frame color encoding processes.
Two generally known prior art systems in the art of the single frame color encoding/decoding processes are illustrated in (1) U.S. Pat. No. 3,378,633, issued to A. Macovski, and entitled MONOCHROME PHOTOGRAPHY SYSTEM FOR COLOR TELEVISION, and (2) U.S. Pat. No. 3,573,353, issued to F. C. Henriques, et al., and entitled OPTICAL DETECTION SYSTEM AND METHOD FOR SPATIAL FILTERING. In the Macovski system, the color content of the scene is encoded on a transparency film chain on separate spatial carriers of low enough frequency to be resolvable by an ordinary single tube television camera, but still of high enough frequency to embrace most of the significant picture detail in the scene. During playback the transparency may be directly imaged on the photoelectrode of the single tube television camera. The electron beam of the camera, scanning the photoelectrode image, converts the spatial carriers of the image into the temporal electrical carriers of corresponding frequency. The frequency selective circuit is coupled to the output electrode of the camera for obtaining separate signals representative of individual components of the color content of the scene. The difficulty with the Macovski system is that during playback the film jitter is translated into the frame-to-frame misalignment of the spatial carriers imaged on the photoelectrode, and thereby precipitating a color washout.
In the Henriques system, color content of the scene is encoded on a transparency film chain on separate spatial carriers of high frequency and different orientations. To reconstruct the color scene, the white light waves, modulated by the high frequency spatial carriers of the transparency, are brought to a focus in the Fourier transform plane. In the transform plane a diffraction pattern corresponding to the spatial frequencies of the transparency appears, with the individual color components occupying different parts of the pattern. The frequencies and orientations of the spatial carriers of the transparency are chosen to ensure a relatively easy identification of various parts of the diffraction pattern. It is noted that the selection of high spatial frequencies, to ensure relatively wide separation of the diffraction orders, would inevitably result in the choice of frequencies beyond the resolution capability of ordinary television cameras and certainly far above the resolution capability of a normal human eye. The zeroth order diffraction generally contains color mixture information, and is preferably masked. The first order diffractions, containing individual color components of the scene, are covered with appropriate color filters. For example, the light containing red component is filtered through a red filter, and so on. The filtered light may be directly imaged on the photoelectrodes of a color television camera. The difficulty with the Henriques system is that it requires a color television camera for color reproduction. In the Henriques system it is not practical to use a single tube television camera with a frequency selective circuit, as in the Macovski system; because, as indicated above, the high frequency spatial carriers needed in the Henriques system are generally beyond the resolution capability of an ordinary television camera. Moreover, even if one assumes, arguendo, that an economical television camera were available with sufficient resolution capability to overcome the above difficulty, unfortunately, the problem of color washout due to film jitter still remains in the Henriques system.